In accordance with a standard method for determining the calorific value of a solid fuel sample recommended by the American National Standard Institute, ANSI/ASTM D 3286-77, a complicated apparatus is employed which requires careful control and maintenance of temperatures in a water "jacket and in the calorimeter vessel in which the combustion bomb is immersed in water. It is not uncommon for such equipment to require water heaters, water coolers along with several valves and pumps to maintain the temperature and the recommended difference in temperature between the calorimeter vessel and the water jacket before the sample can be combusted. It is also recommended that the equipment be set up and used in a special draft free room which is maintained at a constant temperature and that the water in the calorimeter vessel surrounding the bomb be one or more degrees below the ambient water temperature of the water in the water jacket. This adds a further complication in maintaining the temperature difference before the sample is combusted.
In order to determine the calorific value of the sample, the heat given up by the combustion bomb, due to the complete combustion of the sample in an oxygen atmosphere, is equal to the temperature increases of the water in the calorimeter vessel when properly corrected for the heat capacity of the calorimeter and for heat transfer losses. The most common formula used to determine the correct temperature change in the bucket containing the bomb is that developed by Regnault-Pfaundler in 1866. This formula requires that the temperature of the water surrounding the bomb be carefully monitored for several minutes before the sample is combusted to determine when the rate of change of temperature of the water has become constant. At this time the sample can be combusted in the bomb which causes the water temperature about the bomb to rise. The temperature must again be monitored carefully to determine when the temperature has gone through its peak and has begun to cool at a constant rate. The determination of the constant rate of temperature change both before and after the sample burn is critical to the calculation. Precise determination of the rate of change of the temperature requires careful, periodic temperature measurements over several minutes in order to accurately measure each rate of change. It can be seen from the above that the standard process for determining the calorific value of a sample requires a special room, a complicated assembly of equipment and a extended period of time to precisely measure the temperatures in order to determine the rate of change of the temperature which is critical to the final calculation.